The invention described herein arose in the course of, or under, Contract No. DE-AC03-SF00098 between the United States Department of Energy and the University of California for the operation of the Ernest Orlando Lawrence Berkeley National Laboratory. The Government may have rights to the invention.
1. Field of the Invention
This invention relates to semiconductor nanocrystal probes for biological applications wherein the probes include a plurality of semiconductor nanocrystals capable of providing a detectable signal in response to exposure to energy.
2. Description of the Related Art
Fluorescent labeling of biological systems is a well known analytical tool used in modern biotechnology as well as analytical chemistry. Applications for such fluorescent labeling include technologies such as medical (and non-medical) fluorescence microscopy, histology, flow cytometry, fluorescence in-situ hybridization (medical assays and research), DNA sequencing, immuno-assays, binding assays, separation, etc.
Conventionally, such fluorescent labeling involves the use of an organic dye molecule bonded to a moiety which, in turn, selectively bonds to a particular biological system, the presence of which is then identified by excitation of the dye molecule to cause it to fluoresce. There are a number of problems with such an analytical system. In the first place, the emission of light of visible wavelengths from an excited dye molecule usually is characterized by the presence of a broad emission spectrum as well as a broad tail of emissions on the red side of the spectrum, i.e., the entire emission spectrum is rather broad. As a result, there is a severe limitation on the number of different color organic dye molecules which may be utilized simultaneously or sequentially in an analysis since it is difficult to either simultaneously or even non-simultaneously detect or discriminate between the presence of a number of different detectable substances due to the broad spectrum emissions and emission tails of the labeling molecules. Another problem is that most dye molecules have a relatively narrow absorption spectrum, thus requiring either multiple excitation beams used either in tandem or sequentially for multiple wavelength probes, or else a broad spectrum excitation source which is sequentially used with different filters for sequential excitation of a series of probes respectively excited at different wavelengths.
Another problem frequently encountered with existing dye molecule labels is that of photostability. Available fluorescent molecules bleach, or irreversibly cease to emit light, under repeated excitation (104-108 cycles of absorption/emission). These problems are often surmounted by minimizing the amount of time that the sample is exposed to light, and by removing oxygen and/or other radical species from the sample.
In addition, the probe tools used for the study of systems by electron microscopy techniques are completely different from the probes used for study by fluorescence. Thus, it is not possible to label a material with a single type of probe for both electron microscopy and for fluorescence.
It would, therefore, be desirable to provide a stable probe material for biological applications preferably having a wide absorption band and capable of providing a detectable signal in response to exposure to energy, without the presence of the large red emission tails characteristic of dye molecules (thereby permitting the simultaneous use of a number of such probe materials, each, for example, emitting light of a different narrow wavelength band) and/or capable of scattering or diffracting radiation. It would also be equally desirable to provide a single, stable probe material which can be used to image the same sample by both light and electron microscopy.
The invention comprises a semiconductor nanocrystal compound capable of linking to one or more affinity molecules to form a semiconductor nanocrystal probe. The semiconductor nanocrystal compound comprises one or more semiconductor nanocrystals and one or more first linking agents. The one or more semiconductor nanocrystals are capable of providing a detectable signal in response to exposure to energy, wherein such a response may include emission and/or absorption and/or scattering or diffraction of the energy to which the one or more semiconductor nanocrystals are exposed. In addition to or as an alternative to providing a detectable signal, the one or more semiconductor nanocrystals may transfer energy to one or more proximal structures in response to exposure to energy. The one or more first linking agents have a first portion linked to one or more semiconductor nanocrystals and a second portion capable of linking either to one or more second linking agents or to one or more affinity molecules.
The invention further comprises a semiconductor nanocrystal probe formed either by (1) linking one or more of the above described semiconductor nanocrystal compounds to one or more affinity molecules; or (2) linking one or more of the above described semiconductor nanocrystal compounds to one or more second linking agents and linking the one or more second linking agents to one or more affinity molecules, wherein the one or more affinity molecules are capable of bonding to one or more detectable substances in a material. As a result, the semiconductor nanocrystal probe, in one embodiment, is capable of absorbing energy from either a particle beam or an electromagnetic radiation source (of broad or narrow bandwidth), and is capable of emitting detectable electromagnetic radiation in a narrow wavelength band when so excited; while in another embodiment the amount of energy from either a particle beam or an electromagnetic radiation source (of broad or narrow bandwidth) which is absorbed, or scattered, or diffracted by the semiconductor nanocrystal probe, is detectable, i.e., the change in absorption, scattering, or diffraction is detectable. In yet another embodiment, the semiconductor nanocrystal probe is capable of receiving energy transferred from a proximal source and/or transferring energy to one or more proximal structures in response to exposure to energy.
The invention also comprises a process for making the semiconductor nanocrystal compound and for making the semiconductor nanocrystal probe comprising the semiconductor nanocrystal compound linked to one or more affinity molecules capable of bonding to one or more detectable substances. The semiconductor nanocrystal probe of the invention is stable with respect to repeated excitation by light, or exposure to elevated temperatures, or exposure to oxygen or other radicals.
The invention further comprises a process for treating a material, such as a biological material, to determine the presence of a detectable substance in the material, which comprises a step of contacting the material to be treated, with the semiconductor nanocrystal probe, an optional step of removing from the material the semiconductor nanocrystal probes not bonded to the detectable substance, and then a step of exposing the material to energy from, for example, either an electromagnetic radiation source (of broad or narrow bandwidth) or a particle beam. The presence of the detectable substance in the material is then determined by a step of detecting the signal provided by the semiconductor nanocrystal probe in response to exposure to energy. This may be accomplished, for example, either by measuring the absorption of energy by the semiconductor nanocrystal probe and/or detecting the emission of radiation of a narrow wavelength band by the semiconductor nanocrystal probe and/or detecting the scattering or diffraction of energy by the semiconductor nanocrystal probe, indicative (in either case) of the presence of the semiconductor nanocrystal probe bonded to the detectable substance in the material.
The invention further comprises a process for treating a material, such as a biological material with a semiconductor nanocrystal probe which is used to transfer energy to one or more proximal structures. This process comprises a step of contacting the material to be treated, with the semiconductor nanocrystal probe, an optional step of removing from the material portions of the semiconductor nanocrystal probe not bonded to the detectable substance, and then a step of exposing the material to energy from, for example, either an electromagnetic radiation source (of broad or narrow bandwidth) or a particle beam. This is followed by a step of energy transfer from the semiconductor nanocrystal probe to one or more proximal structures which may, in response to the energy transfer, either provide a detectable signal, undergo chemical or conformational changes, or transfer energy to one or more second proximal structures.
The use of the semiconductor nanocrystal probe in the treatment of a material to either provide a detectable signal or transfer energy to a proximal structure may be applied to a plurality of medical and non-medical biological applications. Exemplary applications of the semiconductor nanocrystal probe include: use as a detector of substances on the surface or interior of cells in flow cytometry; use in a plurality of methods for detecting nucleic acid sequences by hybridization, such as fluorescence in-situ hybridization (particularly when the semiconductor nanocrystal probe has been modified in a polymerase chain reaction); or use to transfer energy which may cause the release of a cytotoxic molecule or transfer of heat energy, either of which may result in death of specifically targeted cells. Another use of the semiconductor nanocrystal probe is as a precursor which is treated to synthetic steps which result in a modified semiconductor nanocrystal probe (as in the case of modification by polymerase chain reaction).